The invention relates to a driver assistance system in a motor vehicle and to a correspondingly configured method.
In motor vehicles with driver assistance systems by means of which, in particular, a predefined speed or a predefined distance from the vehicle traveling ahead is to be constantly maintained, methods are already known by means of which a drive system and/or a wheel brake system are actuated in order to reach specific driver assistance goals.
DE 10 2007 006 501 A1 and DE 10 2004 017 115 A1 have already disclosed fuel-saving operating modes for cruise control systems by means of which generally a relatively large control error from the target vehicle speed is permitted. In this context, what is referred to as a coasting mode can also be activated in which an interruption in the transmission of power is brought about, in particular by opening a clutch at or in the transmission. During a coasting mode, the drive engine can also be switched off in order to reduce the consumption of fuel. The coasting mode is ended when the lower permitted threshold of the control error is reached.
DE 10 2010 031 382 A1 discloses a driver assistance system in a motor vehicle by means of which, when the cruise control is activated, a predefined speed or a predefined distance from the vehicle traveling ahead is maintained essentially constantly, and wherein an operating strategy which is optimum in terms of energy, with maximum possible integration of the coasting mode and overrun mode is carried out in order to attain minimum fuel consumption as a function of map-based data of a navigation system. The coasting mode is also switched off when the cruise control is deactivated if the distance from a vehicle traveling ahead is too short or if activation of the brake pedal is to be expected.
Vehicles with cruise control systems which switch into the coasting mode when predetermined conditions apply are commercially available. The coasting mode is exited when the vehicle accelerates, at the latest when a maximum permissible speed is reached.
DE 197 07 140 C1 also discloses a method and a device which increments or decrements a counter reading on the basis of the acceleration behavior of the vehicle and determination of whether a braking device is activated, and starts or ends a coasting mode as a function of the counter reading.
An object of the invention is to improve further a driver assistance system of the type mentioned at the beginning and a corresponding method for controlling a driver assistance system which is designed to perform cruise control, with respect to reducing the fuel consumption and improving the convenience.
The invention is based on a basically known cruise control system with a coasting mode which is permitted and can be actuated in a targeted fashion. When the cruise control is active and the coasting mode is active, the speed is intended to deviate only slightly from the target speed despite the coasting mode. Since the vehicle can accelerate owing to external influences (e.g. traveling downhill) in the coasting mode during which no power is transmitted, the permitted tolerance band around the target speed is, under certain circumstances, departed from in the upward direction, which in the prior art causes the coasting mode to be ended and brings about a simultaneous change into the overrun mode and, under certain circumstances, even into the braking mode. This in turn leads to a situation in which the initiated coasting phases can be very short, which can be perceived by the driver as inefficient and uncomfortable.
The invention is based on the idea of maintaining the coasting mode which has been activated during cruise control for as long as possible, in order thereby to give the driver a driving sensation which is efficient in terms of energy and comfortable.
With the inventive driver assistance system in a motor vehicle, which, when the cruise control is activated, maintains a predefined target speed or a predefined distance from the vehicle traveling ahead essentially constantly by means of an electronic control device and sensors connected thereto, the control device is configured according to the invention, in particular, by corresponding programming and by necessary interfaces to other control devices, in such a way that when a coasting mode is present with the cruise control activated the current speed is acquired by means of sensors, and despite a target-speed-dependent, maximum permissible speed (e.g. upper limit of a permitted tolerance band) for the cruise control being reached the coasting mode is maintained.
The target-speed-dependent maximum permissible speed can deviate from the target speed by a permanently or variably predefined value or can be identical to the target speed.
So that, despite the coasting mode being maintained or retained when the maximum permissible speed is reached, this threshold is not exceeded, the control device is advantageously configured to bring about an automatic braking intervention while maintaining the coasting mode when a coasting mode is present with the cruise control activated and the maximum permissible speed is reached or exceeded, i.e. the control device brings about an automatic braking intervention with the coasting mode (still) active, which is, in particular, configured or brought about in such a way that the maximum permissible speed (or a speed threshold which is set below the maximum permissible speed) is reached again and/or not exceeded.
Basically, the coasting mode can be exited e.g. when the brake pedal is activated. Likewise, the coasting mode can be exited with the cruise control active and the brake pedal not activated (and if appropriate when the maximum permissible speed is reached), for energetic reasons or for reasons relating to comfort, if it is no longer appropriate to reach or maintain the maximum permissible speed while maintaining the coasting mode. In particular, when a coasting mode is present with the cruise control activated it is therefore possible to exit the coasting mode when a braking torque which is required, or which would be requested, to reach or maintain the maximum permissible speed exceeds a predefined absolute braking torque threshold.
In analogous fashion to this, when a coasting mode is present with the cruise control activated (with the brake pedal not activated) the coasting mode can also be exited when a deceleration of the vehicle which is required, or which would be requested, to reach or maintain the maximum permissible speed exceeds a predefined deceleration threshold.
A corresponding method for controlling the driver assistance system can be embodied in an analogous fashion to the inventive driver assistance system proposed here, in that, when a coasting mode is present with the cruise control activated the current speed is acquired by means of the sensors, and despite a target-speed-dependent, maximum permissible speed being reached the coasting mode is maintained.
Further advantageous refinements of the driver assistance system according to the invention also apply to the method according to the invention which can be implemented in a suitable control device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.